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hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="从入门到放弃"></span><header class="post-header"><h2 class="post-title" itemprop="name headline">【从入门到放弃-PHP】foreach 引用的坑</h2><div class="post-meta"><span class="post-time"><span class="post-meta-item-icon"><i class="fa fa-calendar-o"></i></span> <span class="post-meta-item-text">发表于</span> <time title="创建于" itemprop="dateCreated datePublished" datetime="2019-05-26T13:18:44+08:00">2019-05-26</time></span> <span class="post-category"><span class="post-meta-divider">|</span><span class="post-meta-item-icon"><i class="fa fa-folder-o"></i></span> <span class="post-meta-item-text">分类于</span> <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/个人学习/" itemprop="url" rel="index"><span itemprop="name">个人学习</span></a></span></span> <span class="post-comments-count"><span class="post-meta-divider">|</span><span class="post-meta-item-icon"><i class="fa fa-comment-o"></i></span><a href="/76b41bca.html#comments" itemprop="discussionUrl"><span class="post-comments-count valine-comment-count" data-xid="/76b41bca.html" itemprop="commentCount"></span></a></span> <span class="post-meta-divider">|</span><span class="page-pv"><i class="fa fa-file-o"></i> 浏览<span class="busuanzi-value" id="busuanzi_value_page_pv"></span></span><div class="post-wordcount"><span class="post-meta-item-icon"><i class="fa fa-file-word-o"></i></span> <span class="post-meta-item-text">字数统计:</span> <span title="字数统计">1.7k</span> <span class="post-meta-divider">|</span><span class="post-meta-item-icon"><i class="fa fa-clock-o"></i></span> <span class="post-meta-item-text">阅读时长 ≈</span> <span title="阅读时长">7</span></div></div></header><div class="post-body" itemprop="articleBody"><h2 id="背景描述"><a href="#背景描述" class="headerlink" title="背景描述"></a>背景描述</h2><p>先看一段代码。<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line"><span class="comment">/*$arr = [</span></span><br><span class="line"><span class="comment"> 'jack' => '20',</span></span><br><span class="line"><span class="comment"> 'tom' => '21',</span></span><br><span class="line"><span class="comment"> 'marry' => '54',</span></span><br><span class="line"><span class="comment"> 'less' => '23'</span></span><br><span class="line"><span class="comment">];</span></span><br><span class="line"><span class="comment">$b = &$arr['jack'];</span></span><br><span class="line"><span class="comment">$a = $arr;</span></span><br><span class="line"><span class="comment">$b = 30;</span></span><br><span class="line"><span class="comment">var_dump($a);</span></span><br><span class="line"><span class="comment">$str = '20';</span></span><br><span class="line"><span class="comment">$c = &$str;</span></span><br><span class="line"><span class="comment">$d = $str;</span></span><br><span class="line"><span class="comment">$c = 30;</span></span><br><span class="line"><span class="comment">var_dump($d);*/</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> &$val) {</span><br><span class="line"> <span class="keyword">echo</span> $val;</span><br><span class="line">}</span><br><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> $val) {</span><br><span class="line"> <span class="keyword">echo</span> $val;</span><br><span class="line">}</span><br><span class="line">print_r($arr);</span><br></pre></td></tr></table></figure><p></p><p>想一下应该输出什么呢？</p><p>运行一下脚本，真实结果和你想的是否一致呢？</p> <img src="/76b41bca/1.png"><p>在foreach中使用了引用后再次foreach发现$arr[‘less’]的值变成了54，常规理解应该是23才对。</p><p>猜测可能是因为使用引用导致该值变为54 但本着知其然更要知其所以然 我们一起追一下php源码 是什么原因导致的</p><h2 id="环境准备"><a href="#环境准备" class="headerlink" title="环境准备"></a>环境准备</h2><p>工欲善其事必先利其器，先下载调试工具及源码</p><h3 id="下载Visual-Studio-2017，并安装"><a href="#下载Visual-Studio-2017，并安装" class="headerlink" title="下载Visual Studio 2017，并安装"></a>下载Visual Studio 2017，并安装</h3><p>下载地址：<a href="https://www.visualstudio.com/zh-hans/downloads/" rel="external nofollow noopener noreferrer" target="_blank">https://www.visualstudio.com/zh-hans/downloads/</a></p><h3 id="下载php源码"><a href="#下载php源码" class="headerlink" title="下载php源码"></a>下载php源码</h3><p><a href="http://cn2.php.net/distributions/php-7.0.27.tar.bz2" rel="external nofollow noopener noreferrer" target="_blank">http://cn2.php.net/distributions/php-7.0.27.tar.bz2</a></p><h3 id="从文件夹创建解决方案"><a href="#从文件夹创建解决方案" class="headerlink" title="从文件夹创建解决方案"></a>从文件夹创建解决方案</h3><p>创建成功后如下图所示</p> <img src="/76b41bca/2.png"><h2 id="源码追踪"><a href="#源码追踪" class="headerlink" title="源码追踪"></a>源码追踪</h2><h3 id="先搜索关键字foreach"><a href="#先搜索关键字foreach" class="headerlink" title="先搜索关键字foreach"></a>先搜索关键字foreach</h3><img src="/76b41bca/3.png"><p>可以在zend_language_parser.c 中看到， 语法解析时 foreach会当做T_FOREACH</p> <img src="/76b41bca/4.png"><p>在zend_language_parser.y可以看到语法解析的具体方式</p> <img src="/76b41bca/5.png"><p>ZEND_AST_FOREACH</p> <img src="/76b41bca/6.png"><p>查找zend_ast_create</p> <img src="/76b41bca/7.png"><p>zend_ast.c中：</p> <img src="/76b41bca/8.png"><p>zend_ast_create 函数是创建一个抽象语法树（abstract syntax tree）返回的zend_ast结构如下：</p> <img src="/76b41bca/9.png"><p>具体的赋值操作如下：</p> <img src="/76b41bca/10.png"><p>接下来在zend_compile.c中根据抽象语法树生成opcode：</p> <img src="/76b41bca/11.png"><p>通过上图及语法解析的分析可知，foreach在编译阶段会生成如上图的四个zend_ast节点，分别表示：要遍历的数组或对象expr_ast，要遍历的value value_ast，要遍历的key key_ast，循环体stmt_ast<br>如：</p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">$arr = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];</span><br><span class="line"></span><br><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> $key => $val) {</span><br><span class="line"> <span class="keyword">echo</span> $val;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>expr_ast 是可理解为是$arr编译时对应的ast结构</p><p>value_ast对应$val</p><p>key_ast对应$key</p><p>stmt_ast对应”echo $val;”</p> <img src="/76b41bca/12.png"><p>copy一份要遍历的数组或对象，如果是引用则把原数组或对象设为引用类型<br>如：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> $k => $v) {</span><br><span class="line"> <span class="keyword">echo</span> $v;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>copy一份$arr用于遍历，从arData的首元素起，把bucket.zval.value赋值给$v,把bucket.h或key赋值给$k，然后将下一个元素的位置记录在zval.u2.fe_iter_idx中，下次遍历从该位置开始</p><p>当u2.fe_iter_idex到了arData的末尾则遍历结束并销毁copy的$arr副本</p> <img src="/76b41bca/13.png"><p>如果$v是引用 则在循环前，将原$arr设置为引用类型 即：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> $k => &$v) {</span><br><span class="line"> <span class="keyword">echo</span> $v;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/14.png"> <img src="/76b41bca/15.png"><ul><li>编译copy的数组、对象操作的指令：增加一条opcode指令 ZEND_FE_RESET_R（如果value是引用则用ZEND_FE_RESET_RW） 。执行时如果发现遍历的不是数组、对象 则抛出一个warning，然后跳出循环。</li><li>编译fetch数组、对象当前单元key 、value的opcode : ZEND_FE_FETCH_R（如果value是引用则用ZEND_FE_FETCH_RW）。此opcode需要知道当遍历到达数组末尾时跳出遍历的位置。此外还会对key和value分配他们在内存中的位置，如果value不是一CV个变量，还会编译其它操作的opcode</li><li>如果定义了key，则会编译一条opcode，对key进行赋值</li><li>编译循环体statement</li><li>编译跳回遍历开始时的opcode，一次遍历结束后跳到步骤2编译的opcode进行下次遍历</li><li>设置步骤1、2两条opcode如果出错要跳到的opcode</li><li>结束循环 编译ZEND_FE_FREE用于释放1中copy的数组或对象<h2 id="结论分析"><a href="#结论分析" class="headerlink" title="结论分析"></a>结论分析</h2>编译后的结构：</li></ul> <img src="/76b41bca/16.png"><p>运行时步骤：</p><ul><li>(1) 执行ZEND_FE_RESET_R，过程上面已经介绍了；</li><li>(2) 执行ZEND_FE_FETCH_R，此opcode的操作主要有三个：检查遍历位置是否到达末尾、将数组元素的value赋值给$value、将数组元素的key赋值给一个临时变量(注意与value不同)；</li><li>(3) 如果定义了key则执行ZEND_ASSIGN，将key的值从临时变量赋值给$key，否则跳到步骤(4)；</li><li>(4) 执行循环体的statement；</li><li>(5) 执行ZEND_JMPNZ跳回步骤(2)；</li><li>(6) 遍历结束后执行ZEND_FE_FREE释放数组。</li></ul><p>因此根据上面的分析：赋值的核心操作是ZEND_FE_FETCH_RW</p><p>上面的例子可等价于<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$val = &$arr[<span class="string">'jack'</span>];</span><br><span class="line">$val = &$arr[<span class="string">'tom'</span>];</span><br><span class="line">$val = &$arr[<span class="string">'marry'</span>];</span><br><span class="line">$val = &$arr[<span class="string">'less'</span>];</span><br><span class="line">$val = $arr[<span class="string">'jack'</span>];</span><br><span class="line">$val = $arr[<span class="string">'tom'</span>];</span><br><span class="line">$val = $arr[<span class="string">'marry'</span>];</span><br><span class="line">$val = $arr[<span class="string">'less'</span>];</span><br><span class="line">print_r($arr);</span><br></pre></td></tr></table></figure><p></p><p>等价于：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$val = &$arr[<span class="string">'less'</span>]; (<span class="number">23</span>)</span><br><span class="line">$val = $arr[<span class="string">'marry'</span>]; (<span class="number">54</span>，并且此时因为引用 $arr[<span class="string">'less'</span>]也变为<span class="number">54</span>了)</span><br><span class="line">$val = $arr[<span class="string">'less'</span>]; (<span class="number">54</span>)</span><br><span class="line">print_r($arr);</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/17.png"><p>因此 为了避免出现不必要的错误，建议在使用完&后，unset掉变量以取消对地址的引用</p><h3 id="思维发散："><a href="#思维发散：" class="headerlink" title="思维发散："></a>思维发散：</h3><p>针对以上情况，如果不取消对变量的引用，而是将数组赋值给一个新的变量再foreach。是否可行？</p><p>先看一段代码：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$str = <span class="string">'20'</span>;</span><br><span class="line">$c = &$str;</span><br><span class="line">$a = $str;</span><br><span class="line">$c = <span class="number">30</span>;</span><br><span class="line">var_dump($a);</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/18.png"><p>输出20 没有任何问题<br>如果换成数组：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$b = &$arr;</span><br><span class="line">$a = $arr;</span><br><span class="line">$b[<span class="string">'jack'</span>] = <span class="number">30</span>;</span><br><span class="line">var_dump($a);</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/19.png"><p>还是20 符合预期<br>但如果这样呢：<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$b = &$arr[<span class="string">'jack'</span>];</span><br><span class="line">$a = $arr;</span><br><span class="line">$b = <span class="number">30</span>;</span><br><span class="line">var_dump($a)</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/20.png"><p>值却变成了30<br>我们加上xdebug_debug_zval看看发生了什么<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$b = &$arr;</span><br><span class="line">$a = $arr;</span><br><span class="line">$b[<span class="string">'jack'</span>] = <span class="number">30</span>;</span><br><span class="line">var_dump($a);</span><br><span class="line">xdebug_debug_zval(<span class="string">'a'</span>);</span><br><span class="line">xdebug_debug_zval(<span class="string">'arr'</span>);</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/21.png"><p>可以看出，直接引用数组， $b = &$arr, $arr 的is_ref是1，refcount是2, 给$a = $arr时，发生分离，$a 与$arr指向不同的zval，$b 与 $arr指向相同的zval，因此给$b[‘jack’] = 30, $a的值不会发生改变<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line">$b = &$arr[<span class="string">'jack'</span>];</span><br><span class="line">$a = $arr;</span><br><span class="line">$b = <span class="number">30</span>;</span><br><span class="line">var_dump($a);</span><br><span class="line">xdebug_debug_zval(<span class="string">'a'</span>);</span><br><span class="line">xdebug_debug_zval(<span class="string">'arr'</span>)</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/22.png"><p>可以看出，对数组中一个元素引用时，数组的is_ref是0，因为$a = $arr 因此refcount是2 ，指向同一个zval，改变$b的值时，因为$arr[‘jack’]是一个引用，zval的值改变，$a和$arr的zval相同，$a[‘jack’]也变为30<br>同理可以回答最开始提出的疑问：如果我不取消对变量的引用，而是将数组赋值给一个新的变量再foreach。是否可行？答：不行。<br></p><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line">$arr = [</span><br><span class="line"> <span class="string">'jack'</span> => <span class="string">'20'</span>,</span><br><span class="line"> <span class="string">'tom'</span> => <span class="string">'21'</span>,</span><br><span class="line"> <span class="string">'marry'</span> => <span class="string">'54'</span>,</span><br><span class="line"> <span class="string">'less'</span> => <span class="string">'23'</span></span><br><span class="line">];</span><br><span class="line"><span class="keyword">foreach</span> ($arr <span class="keyword">as</span> &$val) {</span><br><span class="line"> <span class="keyword">echo</span> $val;</span><br><span class="line">}</span><br><span class="line">$a = $arr;</span><br><span class="line"><span class="keyword">foreach</span> ($a <span class="keyword">as</span> $val) {</span><br><span class="line"> <span class="keyword">echo</span> $val;</span><br><span class="line">}</span><br><span class="line">print_r($a);</span><br></pre></td></tr></table></figure><p></p> <img src="/76b41bca/23.png"><p>因为$arr与$a指向同一份zval，还是会出现$a[‘less’] = 54的结果。因此，在foreach使用完&后，还是unset掉变量 取消对地址的引用再进行下一步操作吧</p><p>参考文献：<br><a href="https://github.com/pangudashu/php7-internal/blob/master/4/loop.md" rel="external nofollow noopener noreferrer" target="_blank">https://github.com/pangudashu/php7-internal/blob/master/4/loop.md</a></p></div><footer class="post-footer"><div class="post-tags"> <a href="/tags/C/" rel="tag"># C++</a> <a href="/tags/PHP/" rel="tag"># PHP</a></div><div class="post-nav"><div class="post-nav-next post-nav-item"><a href="/6e2383f1.html" rel="next" title="【从入门到放弃-MySQL】mysql 数据恢复实战&踩坑记录"><i class="fa fa-chevron-left"></i> 【从入门到放弃-MySQL】mysql 数据恢复实战&踩坑记录</a></div><span class="post-nav-divider"></span><div class="post-nav-prev post-nav-item"> <a href="/76483f54.html" rel="prev" title="【从入门到放弃-Hadoop】Hadoop基础学习">【从入门到放弃-Hadoop】Hadoop基础学习<i class="fa 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class="nav-link" href="#源码追踪"><span class="nav-number">3.</span> <span class="nav-text">源码追踪</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#先搜索关键字foreach"><span class="nav-number">3.1.</span> <span class="nav-text">先搜索关键字foreach</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#结论分析"><span class="nav-number">4.</span> <span class="nav-text">结论分析</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#思维发散："><span class="nav-number">4.1.</span> <span class="nav-text">思维发散：</span></a></li></ol></li></ol></div></div></section></div></aside></div></main><footer id="footer" class="footer"><div class="footer-inner"><div class="copyright">© <span itemprop="copyrightYear">2020</span><span class="with-love"><i class="fa fa-user"></i></span> <span class="author" itemprop="copyrightHolder">AloofJr</span> <span class="post-meta-divider">|</span><span class="post-meta-item-icon"><i 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